Electrolyte Disturbances

Electrolyte disturbances are abnormal plasma concentrations of the body's principal ions — sodium, potassium, calcium, magnesium, and phosphate. They are common in critically and acutely ill patients, can arise from the underlying illness or its treatment, and may produce neurological, cardiac, and neuromuscular consequences that critical care nurses are positioned to recognize and monitor.

Definition

An electrolyte disturbance is an abnormally high or low plasma concentration of one or more of the body's major ions (notably sodium, potassium, calcium, magnesium, and phosphate), reflecting altered intake, distribution, or excretion.

Scope

This entry surveys the major electrolyte abnormalities encountered in critical and emergency care — disorders of sodium (and the closely linked water balance), potassium, calcium, magnesium, and phosphate — and the physiological reasons they matter. It describes the patterns and consequences of these disturbances as reference material and does not provide thresholds or regimens for correcting them in an individual patient.

Core questions

• Which electrolyte disturbances are most common in critically ill patients, and why do they arise?
• How are disorders of sodium concentration related to water balance rather than to sodium content alone?
• What physiological consequences make potassium, calcium, and magnesium disturbances clinically important?

Key concepts

• Hyponatraemia and hypernatraemia
• Plasma sodium as a marker of water balance
• Hypokalaemia and hyperkalaemia
• Calcium, magnesium, and phosphate disorders
• Transcellular ion shifts
• Effects on cardiac and neuromuscular excitability
• Renal handling of electrolytes

Mechanisms

Plasma electrolyte concentrations reflect the balance among intake, internal distribution between fluid compartments, and renal and gastrointestinal excretion. Sodium concentration is governed largely by water balance — regulated through antidiuretic hormone and thirst — so disorders of plasma sodium primarily signal disturbances of water rather than of total body sodium (Knepper et al., 2015; Spasovski et al., 2014). Potassium is predominantly intracellular, and its plasma level is influenced both by total body stores and by acute shifts across cell membranes, with consequences for cardiac and neuromuscular excitability. Calcium, magnesium, and phosphate are similarly regulated by hormonal and renal mechanisms, and metabolic states such as diabetic ketoacidosis perturb several electrolytes at once (Palmer & Clegg, 2015).

Clinical relevance

Electrolyte disturbances are frequently detected in intensive care and emergency patients and can affect cardiac rhythm, consciousness, and muscle function, making their monitoring an important part of critical care nursing. This entry presents the concepts and patterns for educational reference; it is not a guide to diagnosing or correcting electrolyte abnormalities in any specific patient.

Epidemiology

Disorders of sodium and potassium are among the most commonly recorded laboratory abnormalities in hospitalized and critically ill patients, and hyponatraemia in particular is a frequent reason for specialist guidance (Spasovski et al., 2014).

Evidence & guidelines

European clinical practice guidance addresses the diagnosis and treatment of hyponatraemia, the most common electrolyte disorder (Spasovski et al., 2014). Narrative reviews summarize the combined electrolyte and acid-base disturbances seen in metabolic emergencies such as those of diabetes mellitus (Palmer & Clegg, 2015) and the molecular physiology underlying water and sodium balance (Knepper et al., 2015).

Debates

Pace of correcting chronic hyponatraemia

Guidance emphasizes that overly rapid correction of chronic hyponatraemia carries a risk of osmotic demyelination, so the rate of correction is itself a central clinical concern addressed by guidelines.

Seminal works

• spasovski-2014
• palmer-2015
• knepper-2015

Frequently asked questions

Why does the plasma sodium level reflect water balance more than salt intake?

Sodium concentration is the ratio of sodium to body water; because water balance is tightly regulated by antidiuretic hormone and thirst, an abnormal plasma sodium usually indicates a disturbance of water handling rather than of total body sodium.

Why are potassium disturbances dangerous?

Potassium is the main intracellular ion and strongly influences the electrical excitability of cardiac and other excitable tissues, so both low and high plasma potassium can disturb cardiac rhythm and neuromuscular function.